Research Of Integrated Polarization Navigation Sensor Based On Nanowire Gratings

Polarization navigation is a newly developed navigation technology. It has become a research hot spot because of many unique advantages, such as undisturbed by artificial interference, without accumulated error over time, etc. The prototype of polarization navigation sensor normally uses several polarizers with different polarization directions and photodetectors to constitute the polarization sensitive units. The use of discrete devices has the disadvantages of inevitable angular alignment error, increased system size and weight, etc. The application in Aerospace field is restricted. This thesis aims at nanowire grating based integrated polarization navigation sensor. Nanowire gratings have the advantage of small volume, light weight, good capability of integration, etc. It is suitable for integrated polarization sensitive devices. However, there are still some technical issues about fabricating multi-orientated nanowire polarizers and the integration process with photodetectors. In this thesis, some key issues about sub-wavelength wire-grid polarizer were investigated. The calculation theory, analysis about the transmission mechanism, fabrication process and the integration process were studied. The integrated polarization navigation sensor was fabricated and the related performance was tested.The study started with the systematic calculation and analyzation of subwavelength wire polarizer. The rigorous diffraction theory-Rigorous coupled wave analysis theory was studied. The diffraction efficiency of single layer nanowire polarizer was calculated and the physical mechanism of polarization transmission of sub-wavelength metal gratings was analyzed. The qualitative and quantitative analysis based on the equivalent medium theory and the Fabry-Perot resonance theory were presented. The effect of grating material, duty cycle, grating height and grating type on polarization transmission were analyzed in detail.The fabrication process of subwavelength gratings-simutaneous UV and thermal nanoimprint was then studied. The fabrication method of vertical/oblique nanoarray structure was proposed. The strength of the resist was controlled by exposure time, and the stable vertical/oblique nanoarray structure was fabricated after demolding process. Complementary exposure was applied to solidate the resist, and further deformation was avoided. The perpendicular thermal evaporation process was studied and fabrication method of bilayer nanowire structure by using the fabricated vertical nanogratings was investigated.Multi-orientated bilayer nanowire polarizers were fabricated in the same polycarbonate substrate by using nanoimprint lithography. The prototype of polarization navigation sensor based on the multi-orientated bilayer nanowire polarization filters was constructed. Preliminary integration of the polarization navigation sensor was analyzed, and the angular error was tested. The original angular error was calculated to be within ±1°, angular error within ±0.2° was got by using angular error compensation algorithm.Finally, the integration processes of sub-wavelength wire grid polarizers with photodetector were studied. The integration of bilayer nanowire polarizers with photodetector was fabricated by using nanoimprint lithography and metal thermal evaporation process. The single layer nanowire polarizer was fabricated by using nanoimprint lithography and dry etching process. Two kinds of integrated polarization navigation sesors were constructed. The performance of the integrated polarization navigation sensor was tested. The original angular error was measured to be within ±0.8°, angular error within ±0.1° was got by using angular error compensation algorithm.